The present invention refers to a safety valve, and in particular to a pressure relief valve of the type having a valve body with inlet and outlet, a valve seat and a valve member which is spring-loaded in closing direction of the valve seat, for preventing overpressure in plants operating with gaseous and/or vaporous and/or liquid fluids and/or mixtures.
Safety valves of this type are used for example for protection of containers and plants from excessive overpressure by preventing gases, vapors, overheated or undercooled liquids, e.g. water, during simultaneous or successive change between different states of aggregation from exceeding set pressures.
In industrial steam generation plants, a safety valve of this type can be utilized as a pilot valve for use with pressure relief valves operated by a separate fluid system, or directly in smaller plants for protection from excess pressure.
For these applications, spring-loaded pressure relief valves are known which are equipped with auxiliary means for supporting the stroke or lift, e.g. baffle plates, stroke bells (curved baffle plates), or also mechanical expansion bellows. Because of the fact that at critical relief of compressible fluids and variable counterpressures the static pressures change at discharge velocities near sound level to very low absolute pressures, variations of flow conditions cause conventional safety valves to significantly oscillate during occurrence of counterpressures. The use of additional mechanical or hydraulic cushioning devices for compensating an oscillation of the safety valve could not solve this problem.